Improvement in bridges



N.PETERS. PHDTOAUTHUGRAPHER. WASHINGTON. D c,

PATENT CEEICE.

DAvID A. MITCHELL, oE cEIIcAeo, ILLInoIs.

IMPROVEM ENT IN BRIDGES.

Specication forming part of Letters Patent No. 56,777, dated July 31,1866..

To all/whom 'it may concern Be it known that I, DAVID A. MI'rcIIELL, ofChicago, in the county of Cook, State of Illinois, have invented certainnew and useful Improvements in the Construction and Mode of OperatingDraws for Railroad and other Bridges; and I do hereby declare that thefollowing is afull, clear, and exact description of the same, referencebeing had to the accompanying drawings, makingV a part of this speciication, in which- Figure 1 represents a side view or elevation of thebridgestructure. Fig. 2 shows a sectional end View of the towers, thebridge, suspended draw, the truck, and supporting-braces. Fig. 3 is abroken-off section, showing a plan of the suspension frame work andcollarbraces. Fig. 4 shows 'an enlarged end view of one of thecollar-braces. Fig. 5 shows the top view of a movable track forconnecting the draw with the stationary track. Fig. 6 represents a sideview of a broken-off section, the draw passing underl the arch of thetower. Fig. 7 shows an end view of the frame-work which supports thedraw whenopen. Fig. 8 is a broken-off section of a side view with thecables in the framework underneath the railway-track for the truck. Fig.9 shows an end View of the mode of bracing the framework when the truckson which the draw is suspended are placed and made to operate above thecables. Fig. 10 is a similar View, with truck-wheels connected together,showing the bracing outside of the frame-work. Fig. 1l shows a view ofthe same, with double trucks,

to which the draw is suspended. Fig. 12 shows an end section where thesuspended rods are placed on both sides of the frame and cable. Fig. 13shows the Inode of bracing the framework together, with thesuspension-rods for the draw on the outside of the structure,

The object of my invention is to obviate the difficulties of bridgingnavigable rivers which have low banks and extended low lands on one orboth sides, and, from their width and depth or the substance composingthe bottom of the stream, it is impracticable to build piers ortrestle-work, so that ordinarilyconstructed draws cannot easily beplaced and made to operate over their channel; but by my plan ofsuspending the draw a railroadbridge of any length and a draw of anydesired opening can be made effective without building piers in theriver or near the channel.

My invention consists in hanging the drawbridge on frame-work supportedby cables suspended from towers of sufcient height to allow steamers andother iloating river-craft to pass under the supporting-timbers; also,in forming a railway-track above or below the cables for trucks, fromwhich to suspend a movable section or draw-bridge of any desired. spanor opening.

My invention further consists in the construction of collar-braces whichhold the suspended framework in its place, bracing it laterally andhelping to equalize the strain upon the cables at all points, whetherthe draw is open or in its place for a train of cars to pass over; also,in the construction and mode of operating the adjustable frame and trackfor connecting the car-track with the track on the draw.

To enable others skilled in the art to build my suspended draw forrailroad and other bridges, I will describe the construction and thearrangement of the several parts more in detail, referring to theseveral gures in drawings, and to the letters of reference markedthereon.

The same letters indicate the like parts in all of the gures.

The towers A A should be built of solid masonry, they having securefoundations, and elevated in one body up to a level of the grade of theroad.4 Then the towers are divided and built up with two columns, A A',leaving an open space, B, between them, of sufficient width for thetrack and train of cars to pass between them. The open space B may be ofany desired height, the columns A capped off at the top singly; or theymay be arched over and so connected together at the top as to give themthe greatest solidity for securing the ends of the timbers C C, whichform the chord of the framework on which the entire bridge-structure issupported on the suspension-cables D D, they being `fastened and restingon the top of the towers D D', and made to extend far enough to anchorfirmly to other piers or on the banks of the river.

' The upper chord of timbersV C C may be so spliced and bolted togetheras to present a solid mass extending the whole length of the spanbetween the two towers. The Width of the chord C 0 should be such as togive room for the track-timbers c c to be placed in line with both edgesof the chord-timbers C C, directly underneath them, leaving a narrowopening between the track-timbers c c, for the iron rods to pass, onwhich the draw is suspended from the trucks E E.

rIhe main towers A Amay be built at any required distance apart, and ofsuch height as to allow the cables and all of the suspension frame-workto be placed above, out of the reach of smoke-stacks and the masts ofother river-craft. All of the frame-work and braces, being supported bythe cables D D, two or more in number, are held lirmly in their placesby ma improved collar-braces F F, they being connected with the -cablesby the stirrup-bolts ffffj'f, passing over the cables D D and verticallythrough the blocks b b, the timbers C C and c c, and the right-anglefoot or ledge of the collar-braces e e e.

The collar-braces may be made ot' wood suitably jointed together, orthey may be of cast or wrought metal, with a toot or ledge, c c, onwhich the chord-timber c c for the track a, a, on which the trucks EFErun, are supported, they being put on each side of the chord-timbers inpairs, with blocks of timber b b between the ends at the top and eachpair held firmly together by bolts d d and boltszz, which extend throughboth braces just underneath the chord-tim bers C C.

rIhe truck-railway a a being placed on the ledges e e of thecollar-braces F F, they are firmly heldin place by the stirrup-bolts fj' f f, which rest on the cables D D, and, passing through the timbersvertically, are secured by screw-nuts under the ledges e c.

The two chord-timbers C C may be braced and counterbraced by timbers hh, and held by the bolt-rods z' c i, so thatvery little lateral motionor vibration can be produced, and the structure may also be stayed andvibration up or down prevented by the buckle-jointed brace-rods G,fastened to the pier H, and other tension-rods J J, connecting theframe-work with the towers.

The trucks on which the draw is suspended are. mounted on a series ofdouble-hanged carwheels, I I, they being of such dimensions that theywill pass freely between the chordtimbers C C and the track t a, the twosides of the truck-frame E being coupled together by cross timbers andbraces, which fall below the bottom of the collar-braces F, so that theframe-work K will pass freely under them when the truck is operated tomove the draw. To the frame-work K the chain 7c k is attached foroperating the draw, the chain extending over the whole length, from onetower to the other, so that the draw can be operated at either end ofthe bridge by a crank or Wheel, Ii.

To the truck-frame E is suspended the draw M M, which may be builtmostly of timberssillsstringpieces, plates, and braces-secured rmly byiron rods m mand bolts, similar in its construction to an ordinary spanof a railroad-bridge, it having cross-tics n n and the car-track N N,the draw -bridge being suspended on strong iron bars O O, and supportedby angular braces P P P and crossbraces Q Q Q, so that it is preventedfrom yielding laterally, and will always iind its place and bring thetrack in a line with the stationary track when closed for a train ofcars to pass over.

The draw may be so constructed as to occupy only a portion of the spanbetween the towers, as seen in Fig. 1, and draw oft over a stationaryframe-work, R' R, and track, which may be suspended from the structureabove; or it may be supported on a pier, H; or, it' desirable, the drawmay extend the whole length of the span between the towers and be movedoff through one ot' them onto trestle-work, as seen in Fig. 6, Plate No.2.

The draw-bridge passing over the stationary track when opened mustnecessarily be above it, and to connect the track when the draw isclosed I make a section of the track to be raised and lowered bysecuring the stringpieces S S together'by cross-pieces i" o" r, on 1which are one length or section of the iron rails, this frame beinghinged to the ends of the stationary string-pieces T T, so that when letdown for the draw to pass over the frame will rest on the cross-ties t tt but when the draw is closed the frame is raised up by thebalance-weights U U, the cords u u passing over pulleys V until the twotracks come together; then they are rmly supported by a series ofblocks, W W W, hinged to both sides of the string-pieces S, so that theywill shut in under between the timbers S S and the crossties t t t, andthus iirmly support the inclined track, the hinges H H extending uponthe sides of the timbers S, so as to form a support for the rails andguides to place and hold the ends of the rails in a line together. Whenthe draw is to be opened, the hinged supports being coupled together bya connecting-rod, i/ y, are opened to a right angle, which allows thetrack to fall, the blocks W going in between the cross-ties t t t.

Some ofthe gures in Plate No. 2 show modifications of construction whichare embraced in the principle above described, and do not require to gointo a detailed explanation of theseveral parts by letters of reference.

The advantages of my mode of constructing draws for railroad and otherbridges will be readily seen and understood by those familiar withsections of the country where marshy low lands extend a considerabledistance from the rivers, as in the valley of the Mississippi, and manyother navigable rivers in the South and West, where railroads may haveto cross, and can only be bridged, unless a good and efficient draw canbe built, without conflicting seriously with the commercial operationsof the river. In many places the bed of the stream is quicksand, and nogood foundation can be had for building cribs, piers, or driving pilesfor trestle-work, so that-to build ordinaryconstructed draws is whollyimpracticable.

It will be readily seen that by my mode of placing the suspension workso high above the water that any ordinary sailing or steaming craft canpass under, a bridge with a draw of sufficient span can be vbuilt at-anyplace where'towers can be built to support the suspension.

By all of the plans heretofore known and regarded as practicable uponwhich draws for railroad-bridges have been built it has been necessaryto build large piers in the channel ofthe stream, on which the draws arebalanced current in between them that it is very difficult to steerclear of them.

By my plan and mode of construction, as above described, no piers orabutments are required, and the draw can open the entire width of thechannel or river, if desired, which cannot Well be effected by any otherarrangement or mode of constructing draw-bridges.

Having thus fully described my invention and improvements in theprinciple of constructing draws for railroad and other bridges, what lclaim as new, and desire to secure by Letters Patent, is

l. Suspending the draw for bridges from trucks which run on a railwaysupported on frame-work by suspension-cables on towers, placed eitherabove or below the frame-work at a height sufficient to allow steamboatsand other river-craft to pass freely under the structure that supportsthe draw, as herein described.

2. The collar-bracesv F' F, constructed and arranged as and for thepurposes specified.

3. So placing the stirrups, suspension-rods, and angular braces that.the strain upon the draw and the other portion'of the bridge'structureis equalized upon the suspension-cables, in the manner and for thepurpose herein set forth.

D. A. MITCHELL.

Witnesses: A

J. B. WOODRUFF,- EDM. F. BROWN..

